This invention relates to thin film magqnetic read/write heads.
When a write current is applied to a typical thin-film read/write head, the resultinq write field causes the full width of the tip of each pole of the head to be spanned by a sinqle magnetic domain. When the write current is removed, so-called closure domains and central domains are reformed within the head in a confiquration that minimizes the sum of the magnetostatic, anisotropic, and exchanqe enerqy of the magnetic particles in the head. The precise configuration of the reformed domains will depend on, for example, stress from the alumina layers in the vicinity of the permalloy material that forms the head, the iron/nickel ratio in the permalloy composition, defects in the permalloy material, and the profile of the write current as it is reduced to zero. Thus, the domain configuration after a write operation may differ slightly from the domain configuration prior to the write operation.
When the head is used to read data on a track of a magnetic disk, the field qenerated by the data element being read from the disk is passed alonq the pole of the head by slight rotation of the magnetizations in the central domains and small movements of the domain walls, but without alterinq the general domain configuration. The effectiveness of a read operation will depend on the particular domain confiquration that resulted from the most recent write operation.
Viewed at a less microscopic level, the domain configuration determines the head permeability and hence the efficiency with which the head can read data; and the most recent write operation determines the domain configuration. In some cases, the readinq efficiency of a given domain configuration may be so low as to produce multiple symbol and uncorrectable errors and an inability to read header information.